ORAL CIRRI OF SILUROIDS AND ORIGIN OF THE HEAD IN VERTEBRATES. 35 



The nerve supply is from the R. submandibularis which in Siluroids 

 is given off from the R. mandibularis, just at the point of origin of the 

 coronoid process. The Ramus submandibularis then crosses outside 

 the meutomeckelian process to supply the tentacle. At the branching 

 of the R. mandibularis into R. mentalis and submandibularis, the motor 

 nerves to the muscles, moving the mental and submandibular tentacles 

 are given off. A similar disposition of the nerves is described by 

 Gaupp in Amphibia. " In Urodela and Reptilia, the principal portion 

 of the Inframaxillary nerve runs in the canal of the lower jaw, as the 

 Ramus alveolaris, forwards at the upper edge of the Meckelian cartilage, 

 but a branch of this Alveolaris inferior runs down on the outer side of 

 the Meckelian cartilage, and round its lower edge inwards, reaching the 

 inner side after proceeding through a foramen (in Siredon between the 

 dentary and opercular) and then supplies the Mylohyoid." 



" This branch is the Ramus circumflexus, and in the Frog it alone 

 forms the terminal portion of the Inframaxillaris." (Gaupp). 



The R. submandibularis is present in Myxinoids, running, however, 

 along with the mentalis outside the Processus coronoideus and supplying 

 the skin in front of the Meckelian cartilage. This branch possesses a 

 certain resemblance to the Ramus mandibularis externus but never- 

 theless it appears to me to be really the submandibular. 



Meckelian Cartilage. 



The Meckelian Cartilage of Trichomycterus is of an irregular inverted 

 T-shape, the crossbar of the T being horizontal, the coronoid process 

 representing the stem. The process towards the quadrate does not 

 reach the articulation, partly because the cartilage, even at this young 

 stage, has been resorbed after the formation of the os articulare. 

 Probably at no ontogenetic stage was this arm at all massive. The 

 meutomeckelian process is also very short and far from reaching the 

 symphysis, that being formed by the dentary bones only. The Pro- 

 cessus coronoideus proceeds upwards and forwards accompanied by 

 bone. It bears the procartilaginous coronoid piece. The demarcation 

 between the hyaline cartilage of the coronoid process and the precar- 

 tilage of the coronoid piece is quite clear. 



In Callichthys the coronoid process is wanting, and the coronoid 

 piece is rudimentary. The mentomeckelian extends very little forwards 



